In producing crude oil in offshore areas, floating production systems have been used to transfer large volumes of fluids between subsea installations and the water surface. Floating production systems are becoming more attractive as petroleum production extends to water depths beyond the economic and physical limitation of fixed platforms and to distances beyond the economic limits of pipelines. Most floating production systems have wellheads and special production manifolds on or near the ocean floor and processing equipment and storage facilities on a moored floating vessel. Fluid-handling lines, or conduits, are used to transfer hydrocarbons between the subsea wellheads or manifold systems on the ocean floor and the vessel mounted production equipment.
In many production systems, the oil is produced from formations at an elevated temperature, as much as several hundred degrees above the temperature of the surrounding water. The tubing through which the oil is produced is thus subjected to a wide range of temperatures ranging from sea water temperature (during shutdown of operations) to several hundred degrees during production of hot oil. To accommodate this variation in temperature, it is necessary to provide an expansion joint in the production tubing to prevent buckling and possible tubing failure due to expansion and contraction of the tubing. For example, a production tubing 2000 feet long will expand in length approximately 32 inches when heated from 68.degree. F. to 300.degree. F. Such expansion requires an expansion joint for production from a well in deep waters, such as from a tension leg platform.
The production tubing is usually placed in a marine riser which serves as a retainer for tubing failures. Since no reliable seal design is available for marine expansion joints, these joints invariably leak and the riser is subject to filling with oil. Thus, the back-up safety system in effect becomes the primary oil retention vessel. This is a serious compromise with regard to safety and reliability.
It would be desirable to provide a marine riser system which is not subject to these deficiencies.